1. Field of the Invention
This invention relates to an assistance controlling apparatus for a hybrid vehicle which assists the output of the engine by means of the output of a motor.
This application is based on Japanese Patent Application, No. Hei 11-223135 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles which carry motors as power sources for driving the vehicles in addition to engines are known. As a kind of hybrid vehicle, there is a parallel hybrid vehicle which uses the motor as an auxiliary power source which assists the output of the engine. This parallel hybrid vehicle can satisfy the demands of the driver, for example, by charging the battery by deceleration regeneration and securing the remaining charge of the battery during deceleration, while assisting the engine by means of the motor during acceleration.
Such a parallel hybrid vehicle has the following problem. That is to say, there is a possibility that the driver does not notice that the fuel has run out, because the motor assists the output of the engine when the output of the engine is low, even if the fuel for the engine is running out and the output of the engine is low.
In addition, when the fuel is running out and the ratio of the fuel in the fuel-air mixture introduced into the engine is low, the fuel-air mixture does not burn in the engine. In this condition, when the motor assists the output of the engine and the engine is rotated by the force of the motor, the fuel-air mixture which is not burnt is sent to the exhaust system and the catalyst in this exhaust system may be damaged.
That is to say, there is a possibility that the driver does not notice that there is insufficient fuel, even if the fuel for the engine decreases and the output of the engine decreases, because output is assisted by the motor. Therefore, the driver keeps driving without change, the charge of the battery also decreases, and as a result driving becomes impossible.
Accordingly, it is an object of the present invention to provide an assistance controlling apparatus for a hybrid vehicle which can inform the driver that the fuel for the engine is running out and which does not damage the catalyst in the exhaust system of the engine.
According to one aspect of this invention, this object can be attained by an assistance controlling apparatus for a hybrid vehicle comprising an engine (e.g., an engine 1 in the embodiment) which outputs propulsive power for the vehicle; a motor (e.g., a motor 2 in the embodiment) which assists the output of the engine; a remaining quantity detector (e.g., a gasoline remaining quantity detector 7 in the embodiment) which detects whether the remaining quantity of the fuel is under a fixed value or not; and an assistance-restricting unit (e.g., a motor control unit 4 in the embodiment) which restricts the assistance of the output of the engine by the motor when the remaining quantity detector detects that the remaining quantity of the fuel is under the fixed value.
With the above structure, because the assistance-restricting unit restricts output assistance by the motor when the remaining quantity detector detects that the remaining quantity of the fuel is under the fixed quantity, the propulsive power of the vehicle, which is equal to the total output of engine and motor, is restricted, and this can reliably inform the driver of the vehicle that the remaining quantity of fuel is under the fixed value.
In addition, it is also possible to prevent over-discharge of the battery for the motor, as a result of restricting the assistance of the output of the engine by the motor during fuel shortage conditions.
According to another aspect of this invention, an assistance controlling apparatus for a hybrid vehicle comprises an alarm unit (e.g., display unit 8 in the embodiment) which gives an alarm when the remaining quantity detector detects that the remaining quantity of the fuel is under the fixed quantity. Because the display unit displays an alarm that the remaining quantity of the fuel is under the fixed quantity, it can more surely inform the driver of the vehicle that the remaining quantity of the fuel is under the fixed value.
According to another aspect of this invention, the assistance-restricting unit stops the assistance of the output of the engine by the motor when the remaining quantity detector detects that the remaining quantity of the fuel is under the fixed quantity. Accordingly, the fuel-air mixture which becomes thin and impossible to bum due to the shortage of the fuel is not sent to exhaust system by the engine being forced to rotate by the output assistance of the motor, and the catalyst in exhaust system is not damaged. In addition, over-discharge of the battery can also be prevented because the assistance of the output of the engine by the motor is stopped.
According to another aspect of this invention, the assistance-restricting unit reduces the output assistance quantity by the motor gradually, when the remaining quantity detector detects that the remaining quantity of the fuel is under the fixed value. Accordingly, the driver of the vehicle can be safely informed that the remaining quantity of the fuel is under the fixed value. It is also possible to prevent over-discharge of the battery for the motor.